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Full text of "The Cambridge Natural History"

ti                          DISTRIBUTION   IN   THE   PAST                         83
period, groups of animals had often a far wider range than
at present. To-day the Rhinoceroses are limited to Asia and
Africa, and to quite limited parts of the former continent.
In the past, these animals were abundant in Europe and
North America. Wild Horses now have a range which is not
widely different from that of the Rhinoceroses, save that they
extend into the more northern regions of Asia. Their remains
are abundant both in North and South America. The Hippo-
potamus, now confined to Africa, once ranged over Europe,
Madagascar, and India. There were plenty of American and
European Lemurs. Elephants were nearly world-wide in their
range; and, in short, restricted distribution seems to be on the
'whole a characteristic of animals of the present day.
These statements, however, though perfectly true, nnist not
lead to erroneous inferences. It is rather impressed upon the
reader, in books which contain sections dealing with geographical
distribution, that animals on the whole occupy more restricted
areas at present than in the past. There are, however, plenty
of examples of groups of extinct creatures which had, so far as
we know, quite a restricted range. Thus the Toxodonts were
purely South American, as were the Glyptodonts and some other
forms. And, on the other hand, the Cervidae of to-day are as
widely, if not more widely, distributed than at any other time.
The Hares and Rabbits are now nearly universal in range; the
Cats almost so. "We meet with Bovidae, even excluding the Sheep
and Goats, in all the four quarters of the globe, excluding only
South America and, of course, Australia. The Camelidae are still
common to both the Old and the New Worlds.
During certain periods of the Tertiary epoch it is true that
there was more similarity between Europe and North America
than there is at present. It would have been quite necessary to
unite both into a Holarctic area, such as is now insisted upon by
many; but the reasons for this union would then have been
stronger. The fact is, however, that the closer resemblances were
due to the larger number of families of animals which existed
then than now; these have decayed away from both continents,
and allowed the unlikenesses between the mammalian fauna of
both to become evident. But the likenesses which still sur-
vive have led many to associate the two regions closely together.
So far as the history of a genus or family or larger division